Water may contain many different kinds of contaminants including, for example, particulates, harmful chemicals, and microbiological organisms, such as bacteria, parasites, protozoa, and viruses. In a variety of circumstances, at least some of these contaminants should be removed before the water can be deemed potable, i.e., fit to consume as drinking water.
In non-developed countries, there are deadly consequences associated with exposure to contaminated water. At the same time, there are several factors that contribute to contaminated water, including: increasing population densities, increasingly scarce water resources, no water filter utilities, and often, no electricity (including the batteries which are too expensive). In some instances, homes that are next to one another in the same geography may have large variances in the pressure of untreated drinking water available to them. Also, it is common for sources of drinking water to be in close proximity to human and animal waste, such that microbiological contamination is a major health concern. As a result of waterborne microbiological contamination, an estimated six million people die each year, half of which are children under 5 years of age.
In 1987, the U.S. Environmental Protection Agency (EPA) introduced the “Guide Standard and Protocol for Testing Microbiological Water Purifiers”. The protocol establishes minimum requirements regarding the performance of drinking water filter devices that are designed to reduce specific health related contaminants in public or private water supplies. The requirements are that the effluent from a water supply source exhibits 99.99% (or equivalently, 4 log) removal of viruses and 99.9999% (or equivalently, 6 log) removal of bacteria against a challenge. Under the EPA protocol, in the case of viruses, the influent concentration should be 1×107 viruses per liter, and in the case of bacteria, the influent concentration should be 1×108 bacteria per liter. Because of the prevalence of Escherichia coli (E. coli, bacterium) in water supplies, and the risks associated with its consumption, this microorganism is used as the bacterium in the majority of studies. Similarly, the MS-2 bacteriophage (or simply, MS-2 phage) is typically used as the representative microorganism for virus removal because its size and shape (i.e., about 26 nm and icosahedral) are similar to many viruses. Thus, a filter's ability to remove MS-2 bacteriophage demonstrates its ability to remove other viruses.
Thus, water filter devices that can provide the average household with an adequate daily supply of potable water for drinking and cooking when untreated drinking water is contaminated with viruses and bacteria, water is scarce, electricity and batteries are not available, when there are great variances in water pressure within common geographies and when there are periods of little to no water pressure, is of continued interest.